1. Field of the Invention
The invention relates to a REMA objective. This is an objective with which a Reticle Masking (REMA) device is imaged in the plane of the reticle which carries the structured mask for lithography. The region which is lighted on the reticle is thus sharply delimited. The reticle masking device is usually constructed with adjustable blades.
A REMA objective is used in microlithographic projection apparatus (steppers or scanners).
The invention further relates to a partial objective in an illuminating system of a microlithographic projection exposure apparatus; to a REMA objective that has a partial objective of this kind; and to a microlithographic projection exposure apparatus with a partial objective of this kind.
The partial objective comprises a first and a second lens group. If the partial objective is part of a REMA objective the first and second lens group are also referred to herein as intermediate portion and field lens portion of the REMA objective. The partial objective is arranged between an aperture plane and an image plane, an image field to be illuminated being situated in the image plane. The components are arranged centered about an optical axis. Pencils of rays, each with a respective chief ray, enter the partial objective through the aperture plane; the chief rays intersect the optical axis in the region of the aperture plane. The axial distance of the intersection points of the chief rays with the optical axis is here at most 10% of the diameter of the aperture diaphragm. The axial displacement of the intersection points depends on the aberrations of pupil imaging introduced by the portions of the system arranged before the partial objective. Pupil imaging denotes here imaging between pupil planes. The outermost chief ray, which passes through the aperture plane at the maximum angle to the optical axis, strikes the edge of the image field in the image plane. The ray bundle whose chief ray runs along the optical axis defines a central ray bundle. The first lens group then comprises those lenses in which the outermost chief ray has, according to absolute value, smaller ray heights at the lens surfaces than the marginal ray of the central ray bundle. The second lens group comprises those lenses in which the outermost chief ray has, according to absolute value, greater ray heights at the lens surfaces than the marginal ray of the central ray bundle. A lens of the second lens group has an aspheric lens surface here.
2. Description of the Related Art
An illuminating device for a microlithography projection illumination device is known from DE-U-94 09 744 (U.S. Pat. No. 5,646,715) in it there are provided, in the following sequence: light source, shutter, coupling lens (zoom-axicon), glass rod as integrator, reticle masking system, REMA objective for imaging on the reticle the intermediate field plane located in the reticle masking system, containing a first lens group, a pupil intermediate plane, a second lens group, a deflecting prism, a third lens group, and the reticle plane with the reticle. After this there follows a projection objective, which normally reduces and which contains—for example with a non-telecentric input—an internal pupil plane, and then the wafer in the image plane.
In the system according to EP 0 526 242 A1, a objective is first provided after the integrator, here a honeycomb condenser, before the reticle masking system follows. The reticle masking system is optically conjugate to the reticle plane via two lens groups and a mirror, and is thus imaged. Likewise, the diaphragm at the exit of the integrator—the secondary light source—is imaged by the two lens groups and portions of the projection objective on the pupil of the projection objective. Nothing is said there about imaging errors.
A high-aperture catadioptric reduction objective for microlithography is described in the Applicant's WO 95/32446 (U.S. Pat. No. 5,742,436); its embodiment example according to FIG. 3 and Table 2 is exactly matched by the embodiment example of a REMA objective shown in FIG. 1 herein.
The Laid-Open Patent Application DE-A 195 48 805 (U.S. Pat. No. 5,982,558) of Dec. 27, 1995, which was first published after the priority date, describes REMA objectives with exclusively spherical lens surfaces. The embodiment example there has 13 lenses and is very similar in its optical properties to the embodiment example shown herein in FIG. 1. Both the REMA objective of DE-A 195 48 805 (U.S. Pat. No. 5,982,558) and the REMA objective of Figure represent an excellent match, in regard to their pupil function, to the projection objective of WO 95/32446 (U.S. Pat. No. 5,742,436).
U.S. Pat. Nos. 5,742,436, 5,982,558, and 5,646,715 corresponding, respectively, to WO 95/32446, DE-A 195 48 805, and DE-U-94 09 744, are therefore expressly incorporated herein by reference.
A microlithographic projection exposure device is known from DD 292 727, and has a partial objective of the category concerned between a fly's eye condenser and a structure-carrying mask. A projection objective follows the structure-carrying mask in the beam path, and images the structure-carrying mask, diffraction limited, onto a photosensitive substrate. The first lens group of the partial objective corresponds to the collimator in DD 292 727. The second lens group corresponds to a field lens consisting of only one lens. The field lens has an aspheric correction surface here, in order to affect the angular distribution of the chief rays in the image plane of the partial objective such that the image plane of the projection objective is illuminated nearly telecentrically. The aberrations of pupil imaging between the aperture plane of the partial objective and the aperture plane of the projection objective are reduced by the aspheric correcting surface. The possibilities of correction of pupil imaging with the arrangement of DD 292 727 are limited, since the field lens consists of only a single lens with positive refractive power. Moreover, the embodiment has only an image-side numerical aperture of 0.04 and a maximum field height of 71.75 mm.
European Patent Application EP 0 811 865 A2 shows a partial objective, which is arranged between an aperture plane and an image plane. Here not the reticle, but a masking device, is arranged in the image plane of the partial objective, and is imaged onto the reticle by a following objective. Therefore, the partial objective has no direct influence on the distribution of the chief ray angle at the interface between the illuminating device and a following projection objective.
Microstructured components with structure sizes below 0.2 μm can be produced with modern projection objectives. In order to attain these high resolutions, the projection objectives are operated at wavelengths of 248 nm, in particular 193 nm or even 157 nm, and have image-side numerical apertures of greater than 0.65. At the same time, the image field diameter is for the most part greater than 20 mm. The requirements on the optical design for such a projection objective are, therefore, considerable. Besides the field imaging of the reticle onto the photosensitive substrate, the so-called wafer, the pupil imaging is also to be corrected. Thus the forward objective portion, arranged between the object plane and the aperture plane, of a projection objective influences the imaging of the entrance pupil onto the aperture plane, while the rearward objective portion, arranged between aperture plane and image plane, influences the imaging of the aperture plane onto the exit pupil. The aberrations of pupil imaging of the projection objective then become apparent in the distribution of the chief ray angles in the object plane of the projection objective.